Liquid crystal display devices are used in various measuring instruments, automotive panels, word processors, electronic notebooks, printers, computers, television sets, clocks and watches, and advertising boards, as well as clocks and watches and electronic calculators. Typical liquid crystal display modes include a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a vertically aligned (VA) mode characterized by vertical alignment including a thin-film transistor (TFT), and an in-plane switching (IPS)/fringe field switching (FFS) mode characterized by horizontal alignment including a thin-film transistor (TFT).
Liquid crystal materials having a negative dielectric constant anisotropy (Δε) are characteristically used in the IPS mode, an electrically controlled birefringence (ECB) mode, the VA mode, and a color super homeotropic (CSH) mode among such display modes. By contrast, liquid crystal compositions having a positive Δε are used in horizontal alignment displays of the TN mode, the STN mode, and the IPS mode. In recent years, a display drive mode has been reported that includes vertically aligning a liquid crystal composition having a positive Δε under no voltage application and applying an IPS mode/FFS mode electric field to the liquid crystal composition. In all these drive modes, there is a demand for low-voltage drive, high-speed response, and a wide operating temperature range. In other words, there is a demand for a high absolute Δε, a low viscosity (η), and a high nematic phase-isotropic liquid phase transition temperature (Tni). In order to set the product Δn×d of refractive index anisotropy (Δn) and cell gap (d) at a predetermined value, the Δn of a liquid crystal composition must be adjusted in an appropriate range for the cell gap. Furthermore, liquid crystal display devices for use in television sets require a liquid crystal composition with a low γ1 due to the importance of high-speed responsivity. Liquid crystal compositions are generally composed of several to tens of compounds to optimize the Δε and Δn in each display device.
In addition to the demands on the physical properties of liquid crystal compositions, a liquid crystal composition for use in a liquid crystal display device should be stable toward external stimuli, such as water, air, heat, and light. A lack of stability toward external stimuli causes display defects of a liquid crystal display device, such as image sticking or variations in display. A high voltage holding ratio (VHR) is generally believed to be essential to prevent display defects, such as image sticking or variations in display. Thus, it is known that some liquid crystal compositions contain a particular compound in combination with, for example, an antioxidant, an ultraviolet absorber, or a light stabilizer (Patent Literature 1 and Patent Literature 2). Stability toward external stimuli is regarded as important in any application. Thus, further development of a liquid crystal composition that can achieve a high VHR is required.
Furthermore, liquid crystal compositions for use in liquid crystal television sets that require high-speed response need a sufficiently low η, a sufficiently low γ1, a high elastic constant (K33), and a high VHR without a decrease in Δn and Tni. Furthermore, there is a demand for a liquid crystal display device including such a liquid crystal composition with no or few display defects, such as image sticking or variations in display, and with high display quality and a high response speed.